core: change VdsRefreshTimeout to 3 seconds

The current value of 2 seconds is a bit low. The UI refreshes every 5
seconds.
It was agreed to increase this value in order to reduce CPU load.

Change-Id: Id84c8b8bbc939559ff8be4f86b8adbe1ed6f450c
Signed-off-by: Eli Mesika <emesika@redhat.com>
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=908745